Well, no reason to insult those of us who get attached to the casts of these games. Nostalgia isn't intrinsically a bad thing. If a good story can be told, then why not do it? If it can't, then I would agree--it isn't worth doing.
It can't be done, realistically. Maybe with all the resources and all the development time. The fates of our PCs - especially the warden - are too disparate, as are those of most of the NPCs we get attached to. And unfortunately, the nature of Bioware's design process seems to ensure that any cameos related to these characters are inevitably cheap and pointless (Alistair in DA2) or necessarily subject to retcons (Anders, Leliana) which ensure that people will rage forever about how awful the retcons are. Look at Mass Effect - every single cameo they put in there was awkward and pointless.
It's more interesting if they close the book at the end of a given game and move on to pastures new.